Cathodic protection system

ABSTRACT

An impressed current cathodic protection system for a target structure susceptible to corrosion (such as of steel or cast iron) which comprises an inert mixed metal oxide anode surrounded by a tightly packed conductive zone connected to a power supply source and having an input/output regulator to control the flow of current to the target structure. The present invention relates to device and method to provide personal and/or medical details of one or more individuals in the event of an emergency.

FIELD OF THE INVENTION

This invention relates to a cathodic protection system for steelstructures (or cast iron) structures. This invention has particularapplication for cathodic protection of buried and submerged structures(on land and in marine off-shore applications). However, it is also berelevant for other types of structures in which steel (or iron) is asignificant structural component.

BACKGROUND OF THE INVENTION

Steel structures are used widely in industrial structures andinfrastructure due to its strength and tensile properties. However,corrosion is a major problem over time. The use of cathodic protection(CP) using sacrificial anode systems in order to inhibit corrosion ofthese structures is well known. Conventional sacrificial anode systemsare fitted to industrial structures such as pipelines, above groundstorage tanks, underground tanks, and many other structures sited on orburied in the ground. Typically, this is done by attaching a number ofmetal blocks (anodes) of a more active metal such as magnesium to thesteel structure. The more active metal acts as a sacrificial anodepreferentially corroding away. This generates a small amount of DCcurrent. The current output capacity of a magnesium sacrificial anodesystem attached to a pipeline or similar structure is normally 50 mA orless. However, for poorly coated pipelines or structures, anode systemsas high as 1500 mA or greater can be required.

Magnesium anodes are very inefficient. In order to generate 100 mA ofcurrent, one kilogram of magnesium alloy is consumed per year. 55% ofconsumption produces the DC current. The remaining 45% of the corrosionis consumed by self corrosion of the magnesium metal. Accordingly, theelectrical efficiency of the anode is only around 55%. If the anode weredisconnected from the steel structure, it would still naturally wasteaway due to self corrosion.

In order to achieve the DC current output required for corrosionprotection, it is often necessary to fit a number of anodes at any onelocation. For a buried pipeline, anode beds are typically installed attwo to four kilometre intervals at a distance of not more than twometres from the pipeline easement. A typical anode bed is comprised of 5or more anodes in order to generate the requisite current at theinstallation location. Typically, the primary cost for five sacrificialanodes will be in the order of AUD$2,000.00. The installation andcommissioning costs of the anode bed including civil works andcommissioning will typically be in the order of AUD$5,000.00.

A typical magnesium sacrificial anode system has a life expectancy often years. Because many sacrificial anode systems are installed onpipelines often in congested city streets and have to be installed closeto the pipelines. With urban development, the cost to excavate andinstall new anode beds on a ten year cycle is significantly higher.Replacement costs plus extensive excavation costs in congested urbanareas can be in the order of at least AUD$10,000 per site. Forinstallations along a pipeline route, being installed every two to fourkilometers, the accumulated replacement costs over a fifty yearlifecycle of a pipeline can be in the hundreds of thousands of dollars.

The cost to the environment in producing 1 kg of magnesium isapproximately 40 kJ of power. So, apart from being a very inefficientanode material, the carbon footprint to the environment is grosslyunacceptable. The environmental efficiency of a material is largelydetermined by the CO₂ footprint.

CO₂ Footprint:

The production of 1 kg of magnesium generates a CO₂ footprint of 42 kgof CO₂. The annual average magnesium tonnage consumed by the cathodicprotection industry per annum in Australia and New Zealand alone is inexcess of 400 tonnes. This equates to an annual CO₂ footprint of 16,800tonnes of CO₂. Assuming a cost of AUD$23.00 per tonne for CO₂, thisequates to an annual cost to industry before materials of $386,400. Overa fifty year design life, this equates to a CO₂ cost ofAUD$19,320,000.00 (being close to AUD$20,000,000. The environmentalefficiency of a material substitution is largely determined by the CO₂footprint.

SUMMARY OF THE INVENTION

There is disclosed herein an impressed current cathodic protectionsystem for a target structure susceptible to corrosion (such as of steelor cast iron) which comprises an inert mixed metal oxide (hereinafterreferred to as “MMO”) anode surrounded by a tightly packed conductivezone connected to a power supply source and having an input/outputregulator to control the flow of current to the target structure.Preferably, the tightly packed conductive zone is in the form of apowder. In the preferred embodiment the tightly packed conductive zoneis comprised of calcined petroleum coke (semi graphitized carbonparticles). Further, in the preferred embodiment, the system is drivenby a DC power supply stored in a sealed battery cell.

A number of conventional anode materials were considered for thisapplication and rejected. Silicon, iron (chromium), graphite and scrapsteel were all potential materials but considered unlikely to have thedesired life expectancy for the application. Platinised titanium has/hadhistorical technical limitations on voltage. Platinised niobium was notcost competitive. As the life of the anode is critical for cathodicprotection, it was decided that MMO was currently the best availablematerial for this application. An MMO electrode is one in which thesurface contains two or more kinds of metal oxides. One of the metals,usually one or more earth derivatives (such as RuO₂, IrO₂, or PtO_(0.12)conducts electricity and catalyzes the reaction. The amount of this(more expensive) metal is up to 10-12 g per square metre. The othermetal is typically in the form of TiO₂ which does not conduct orcatalyze the reaction, but prevents corrosion of the interior (and ischeaper). The interior of the MMO electrode is typically made oftitanium. The MMO coating is applied to the surface of the titaniumsubstrate to activate the surface.

According to the system of the present invention, the anode issurrounded by a zone of calcined petroleum coke, being a highlyconductive material. This is in the form of a tightly packed powder witha low moisture content. This provides a tightly packed conductive zonearound the anode and effectively increases the active zone of the anode.

According to one form of the invention, the specification for thecalcined petroleum coke is as follows:

Fixed carbon: 99.35%

Ash: 0.6%

Moisture: 0.05%

Volatiles: Nil at 950° C.

Bulk Density: 74 lbs. per cubic foot.

Predominantly round particles.

All particles surface modified for maximum electrical conductivity.

Particle Sizing: Dust free with a maximum particle size of 1 mm.

Minimum calcination temperature of base materials in excess of 1200° C.

Base materials calcined under ISO 9002 quality control.

Surfactants added to assist pumping and settling.

No de-dusting oils used during the manufacture of base particles.

This material was selected as it exhibited the best electricalproperties and reliability under the conditions tested.

In a preferred form of the invention, the anode and surrounding zone ofcalcined petroleum coke is contained within a tubular sleeve which issealed at both ends. The sleeve may be of a permeable synthetic or linencloth, or other suitable material, which is non-degradable in theenvironment in which the anode is to be used. The MMO wire is locatedalong the centre of the sleeve which is sealed at one end. The calcinedpetroleum coke backfill is air blown into the sleeve through the otherend and then sealed. The sleeve which by way of example may be typically(approx 50 mm Diameter×2000 mm and approximately 2 kg in weight) is of acompact design and allows for ease of installation. This is particularlyimportant in congested urban areas where a more compact system isrequired.

The system is designed to be able to produce 50 to 150 mA of currentsubject to suitable conditions (such as soil resistivity). The number ofanodes required to achieve the desired life expectancy will vary fromone to a number of anodes depending upon the soil resistivity.Typically, a number of anodes are placed into a bed. The placement ofthe anode bed will be determined by a range of factors such as safeburial offset or below pipe distances and soil resistivity.

In certain circumstances, where a greater level of currentlifeexpectancy is required, it is possible to effectively increase thecapacity of the system by adding more calcined petroleum coke. This maybe achieved by using a larger sleeve or by adding calcined petroleumcoke to the anode bed excavation (provided that the coke is sufficientlytightly compacted so that the entire bed becomes a working anode bed).

According to a preferred form of the invention, the system is providedwith solar input power generation and battery storage. The batteries arecharged by solar powered cells or panels. These may be mounted byvarious means. These may be mounted on the structure itself or in thecase of a pipeline on a column designed for this purpose which may alsoconveniently house the hardware and service access.

It is anticipated that other alternative forms of environmentallyfriendly or cost effective forms of power supply may be utilized. Thesemay include wind, thermo electric generators (TEGs) or turbinegeneration.

The use of solar or other environmentally friendly forms of powergeneration and storage provides a long-life system with environmentallyfavourable power generation thereby minimizing the environmental impact.It is anticipated that the total CO₂ footprint for the 1.5 mm diameterMMO/TlO₂ anode will be around 0.473 kgsm.

The output power to the structure is controlled by a DC input/outputregulator. Preferably, the system will be capable of operating at anumber of output capacity ranges. Typically, these would be 50, 150, 500and 1000 mA. However, these figures are by way of example only. Therange may vary depending upon the application. Preferably, this wouldalso be provided with lightning and surge protection. Typically, theoutput regulator is approximately 30 mm×80 mm. The output regulator andcontrol circuitry are designed to fit within a small control box whichmay be fitted on the structure or support column or, where applicable,on a structure within close proximity such as a suburban lamppost.

The system design can also accommodate a range of optional monitoringsystems.

The system can accommodate the inclusion of a permanently installedreference cell to allow monitoring of the protection system byconventional manual methods or via an electronic interface or SCADAsystem.

Alternatively, the system can accommodate remote electronic surveillanceand monitoring systems to provide continuous electronic monitoring andreporting via satellite or a GSM communications system. Accordingly, thesystem is capable of reducing the need to travel to sites for inspectionand testing.

Alternatively, the system can also accommodate an automaticallycontrolled output regulated system that incorporates the above referencecells. This may be set during commissioning to allow for a setprotection level and also regulates output in automatic control mode.

The above system utilizes inert anodes that do not galvanically corrodeand increases the active zone of the anode, thus greatly increasing thelife expectancy of the system over those systems currently known and inuse. It is anticipated that the system of the present invention willhave a life of at least 50 years. To accord with the anticipated lifeexpectancy, the anode bed, electronics and related electrical componentsare also all designed to a specification of at least a 50 year lifeexpectancy. The advantage of the above invention over current systems isthat it provides a compact system with a 50 year life expectancy whichis easy to install even in difficult conditions. It is also able to bemodified so as to provide a level of flexibility.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that this invention may be more readily understood and put intopractical effect, a preferred form of the present invention will now bedescribed by way of example with reference to the accompanying drawingswherein:

FIG. 1 is a cross-sectional view of a preferred embodiment of theimpressed current cathodic protection system.

FIG. 2 is a cross-sectional elevational view of a further preferredembodiment of the system of the present invention showing a solarpowered impressed current cathodic protection system and reference cellinstallation.

FIG. 3 is a cross-sectional side view of the embodiment in FIG. 2.

FIG. 4 is a detailed front elevational view of the solar panel andsupporting column, foundation for the solar powered installation inFIGS. 2 and 3 and of the housing for the regulator and controlcircuitry.

FIG. 5 is a further detailed front elevational view of the solar panel,supporting column, foundation and baseplate for the solar poweredinstallation in FIGS. 2 and 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown an impressed current cathodicprotection system for steel (& cast iron?) structures (1) whichcomprises an inert mixed metal oxide (MMO) anode wire (2) surrounded bya zone of calcined petroleum coke (3) contained within a tubular sleeve(4) sealed at both ends (5) and connected via a cable tail (6) to apower supply. Preferably, the system is driven by a DC power supply,which in this embodiment is a sealed battery cell (not shown).

The system also has an output regulator (not shown) to control the flowof current to the target structure.

In this preferred form of the invention, the specification for thecalcined petroleum coke is as follows:

Fixed carbon: 99.35%

Ash: 0.6%

Moisture: 0.05%

Volatiles: Nil at 950° C.

Bulk Density: 74 lbs. per cubic foot.

Predominantly round particles.

All particles surface modified for maximum electrical conductivity.

Particle Sizing: Dust free with a maximum particle size of 1 mm.

Minimum calcination temperature of base materials in excess of 1200° C.

Base materials calcined under ISO 9002 quality control.

Surfactants added to assist pumping and settling.

No de-dusting oils used during the manufacture of base particles.

This material was selected as it exhibited the best electricalproperties and reliability under the conditions tested.

Referring to FIGS. 2 & 3, there is shown an elevational and side viewrespectively of a further preferred embodiment of the cathodicprotection system (which may be comprised of one or a bed of anodes) ofthe present invention. FIGS. 2 and 3 show the placement of the cathodicprotection system (1) and a reference cell (7) relative to pipeline (8),being the target structure in this case. The cathodic protection system(1) and reference cell (7) are embedded in sand (9) at a safe burialdistance from the pipeline (8). This is covered by a layer of rock/freebackfill (10) and generally topped with a finished grade (11). In thisembodiment, the system is provided with solar input power generation.The cathodic protection system is connected by cables (12) to one ormore batteries. The batteries are charged by solar cells on one or moresolar panels (13). These are mounted on a supporting column (14) withbaseplate (15) in concrete foundation (15). The output regulator,control circuitry and service access are located in housing (17) at thebase of the column (14) with access door (18) for ease of access. Adetailed view of the column (14), foundation (16), housing (17) andbaseplate (15) are provided in FIG. 4. Structural components and relatedequipment are manufactured to applicable local building and safetystandards.

In other forms of the invention, it is envisaged that other alternativeforms of environmentally friendly or cost effective forms of powersupply may be utilized. These may include wind, TEGs or turbinegeneration.

It will of course be realized that while the foregoing has been given byway of illustrative example of this invention, all such and othermodifications and variations thereto as would be apparent to personsskilled in the art are deemed to fall within the broad scope and ambitof this invention as is herein set forth.

1. An impressed current cathodic protection system for a targetstructure (susceptible to corrosion) comprising: An inert mixed metaloxide anode surrounded by a tightly packed conductive zone; Connected toa power supply source; and Having an input/output regulator to controlthe flow of current to the target structure.
 2. An impressed currentcathodic protection system for a target structure according to claim 1in which the target structure is of steel;
 3. An impressed currentcathodic protection system for a target structure according to claim 1in which the target structure is of cast iron.
 4. An impressed currentcathodic protection system according to claim 1 wherein the anode iscomprised of a mixed metal oxide (“MMO”).
 5. An impressed currentcathodic protection system according to claim 1, wherein at least one ofthe surface metals in the MMO anode is selected from the earthderivatives.
 6. An impressed current cathodic protection systemaccording to claim 5 wherein at least one of the surface metals in theMMO anode is RuO₂.
 7. An impressed current cathodic protection systemaccording to claim 5 wherein at least one of the surface metals in theMMO anode is IrO₂.
 8. An impressed current cathodic protection systemaccording to claim 5 wherein at least one of the surface metals in theMMO anode is PtO_(0.12).
 9. An impressed current cathodic protectionsystem according to claim 5 wherein the amount of the said metal is upto 10-12 g per square metre.
 10. An impressed current cathodicprotection system claim 4, wherein the other surface metal in the MMOanode is typically in the form of TiO₂
 11. An impressed current cathodicprotection system according to claim 4, in which the interior of the MMOanode is made of a metal which prevents corrosion of the interior
 12. Animpressed current cathodic protection system according to claim 4 inwhich the interior of the MMO anode is made of titanium.
 13. Animpressed current cathodic protection system according to claim 1 inwhich the tightly packed conductive zone effectively increases theactive zone of the anode.
 14. An impressed current cathodic protectionsystem according to claim 1 in which the tightly packed conductive zoneis in the form of a powder with a low moisture content.
 15. An impressedcurrent cathodic protection system according to claim 1 in which thetightly packed conductive zone is comprised of calcined petroleum coke.16. An impressed current cathodic protection system according to claim15 in which the calcined petroleum coke is comprised of: Fixed carbon:99.35% Ash: 0.6% Moisture: 0.05% Volatiles: Nil at 950° C. Bulk Density:74 lbs. per cubic foot. Predominantly round particles. All particlessurface modified for maximum electrical conductivity. Particle Sizing:Dust free with a maximum particle size of 1 mm. Minimum calcinationtemperature of base materials in excess of 1200° C. Base materialscalcined under specified quality control. Surfactants added to assistpumping and settling. No de-dusting oils used during the manufacture ofbase particles.
 17. An impressed current cathodic protection systemaccording to claim 1 in which the anode and surrounding tightly packedconductive zone is contained within a tubular sleeve sealed at bothends.
 18. An impressed current cathodic protection system according toclaim 17 in which the tubular sleeve is comprised of a non degradablepermeable synthetic or linen cloth or other suitable material.
 19. Animpressed current cathodic protection system according to claim 1 inwhich a number of anodes are placed into an anode bed
 20. An impressedcurrent cathodic protection system according to claim 1 wherein thesystem is driven by a DC power supply stored in a sealed battery cell.21. An impressed current cathodic protection system according to claim 1in which the system power supply is provided by means of solar inputpower generation and battery storage.
 22. An impressed current cathodicprotection system according to claim 21 in which the solar input powergeneration is in the form of solar powered cells or panels.
 23. Animpressed current cathodic protection system according to claim 1 inwhich the system power supply is generated by means of wind power. 24.An impressed current cathodic protection system according to claim 1 inwhich the system power supply is generated by means of thermo electricgenerators.
 25. An impressed current cathodic protection systemaccording to claim 1 in which the system power supply is generated bymeans of turbines.
 26. An impressed current cathodic protection systemaccording to claim 1 in which the total CO₂ footprint for the 1.5 mmdiameter MMO/TiO₂ anode will be about 0.473 kgs/m.
 27. An impressedcurrent cathodic protection system according to claim 1 wherein thepower to the structure is controlled by a DC input/output regulator. 28.An impressed current cathodic protection system according to claim 27wherein the system is capable of operating at a number of outputcapacity ranges.
 29. An impressed current cathodic protection systemaccording to according to claim 28 wherein the system is capable ofoperating at about 50, 150, 500 and 1000 mA.
 30. An impressed currentcathodic protection system according to claim 27 wherein theinput/output regulator and control circuitry are designed to fit withina small control box which may be fitted on the structure or supportcolumn or, where applicable, on a structure within close proximity. 31.An impressed current cathodic protection system according to claim 1wherein the system is optionally provided with lightning and surgeprotection.
 32. An impressed current cathodic protection systemaccording to claim 1 wherein the system is optionally provided withmonitoring systems.
 33. An impressed current cathodic protection systemaccording to claim 1 wherein the system is optionally provided with oneor more permanently installed reference cells to allow monitoring of theprotection system by conventional manual methods or via an electronicinterface or SCADA system.
 34. An impressed current cathodic protectionsystem according to claim 1 wherein the system is optionally providedwith a remote electronic surveillance and monitoring system to providecontinuous electronic monitoring and reporting via satellite or a GSMcommunications system.
 35. An impressed current cathodic protectionsystem according to claim 1 wherein the system is optionally providedwith a remote automatically controlled input/output regulated system.36. A method of operating an impressed current cathodic protectionsystem by means of the apparatus disclosed herein with reference to thedescription and drawings.
 37. A method of operating an impressed currentcathodic protection system by means of the apparatus disclosed herein inwhich the total CO₂ footprint for the 1.5 mm diameter MMO/TiO₂ anodewill be about 0.473 kgs/m
 38. A method of operating an impressed currentcathodic protection system by means of the apparatus disclosed hereinwith reference to the description and drawings.